SALT RELATIONS OF VASCULAR PLANTS 



121 



exhibited between ions. Some ions, e.g. iron and manganese, tend to 

 be more concentrated relative to other cations in roots than in shoots, 

 and this is attributable to formation of insoluble inorganic salts (e.g. 

 insoluble phosphates) or organic complexes, which render the ions 

 unavailable for transfer into the shoot. In other cases, however. 



Table 12. Concentrations of Ions in the Xylem Sap of Intact Plants 

 UNDER Conditions of High and Low Transpiration and at Various External 



Salt Concentrations. 

 (From: Russell and Shorrocks, 1959). 



the characteristic distribution of salts between shoots and roots 

 depends on discrimination between ions in the transport of salt out 

 of the root. Potassium ions, for example, move into the shoot, in 

 preference to sodium ions which tend to be left behind to accumulate 

 in the root. This effect is not due to selective absorption of sodium 

 ions into vacuoles of the root cortex cells allowing an excess of 

 potassium ions to move into the stele, at least in barley plants, 

 because excised root systems also exhibit a preference for potassium 



